Prime Minister Narendra Modi met with Thailand Prime Minister Prayut Chan-o-cha here on Thursday.
Prime Minister Modi will address the plenary session of the India-ASEAN commemorative summit later today.
The focus of the summit will be counter-terrorism, security, trade, and connectivity.
All 10 leaders of ASEAN countries will attend the Summit, which marks the 25 years of Indo-ASEAN ties.
Nine ASEAN leaders have already arrived in New Delhi and only Indonesian President Joko Widodo will come today.
In an unprecedented event, all the 10 ASEAN leaders will also be the chief guests at the Republic Day parade tomorrow.
President Ram Nath Kovind will host a banquet in honour of ASEAN leaders. It will be followed by a Leader's Retreat.
The Prime Minister, yesterday, held separate bilateral meetings with leaders of three ASEAN nations - Myanmar, Vietnam and Philippines.
Prime Minister Modi met Myanmar's State Counsellor Aung San Suu Kyi, his Vietnamese counterpart Nguyen Xuan Phuc and Philippines President Rodrigo Roa Duterte.
The Prime Minister will hold a total of nine bilateral meetings with leaders of ASEAN countries on the sidelines of the Summit.